Color display system utilizing biasing means to reduce the effect of misconvergence



Nov. 2, 1965 A. M. MORRELL COLOR DISPLAY SYSTEM UT THE EFFECT OF MISCONVERGENGE Filed Feb. 27, 1962 ILIZING BIASING MEANS TO REDUCE 2 Sheets-Sheet l s ik IMPL M Jiff- .57 w

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n M SN United States Patent O CQLOR DISPLAY SYSTEM UTILIZING BIASING MEANS T REDUCE THE EFFECT 0F MIS- CNVERGENCE Albert M. Morrell, East Petersburg, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed Feb. 27, 1962, Ser. No. 176,045 13 Claims. (Cl. )J8- 5.4)

My invention relates to color display systems, and particularly to an improved method and an improved system employing a multi-gun color tube wherein perfect convergence of the electron beams from the guns is dithcult to establish and maintain. An example of such a color tube is the tri-color kinescope known as the shadowmask color tube, tube type 2lCYP22 being one example.

For some types of color displays, such as displays showing small symbols in diierent colors, a departure from substantially perfect convergence of the electron beams of a tri-color kinescope may seriously degrade the display when the color tube is operated in the usual way. For example, if the symbol to be displayed is a very narrow vertical bar to be displayed in cyan, conventional practice would require that the video signal representing the vertical bar be applied to the blue and lgreen guns. A substantial amount `of horizontal mis-convergence would cause the electron beams from the blue and green guns to write respectively, blue and green bars spaced apart on the screen. A single bar of cyan color would not be obtained.

For a display of three colors only, this kind of diiculty can be avoided. Assume the usual type of television scan with horizontal and vertical beam deflection of the three beams of a color tube. A symbol 'of any one of the three primary colors may be obtained by cutting oft two of the electron beams, lor by having all three beams normally cut off, and having the symbol signal activate one gun. Thus, the blue and green beams may be cut oft" (or only the red beam turned on) to obtain a red symbol. The above-mentioned spaced-apart different color symbols (bars in the example) are absent. A similar situation exists for the presentation of a blue symbol or a green symbol.

However, when a symbol of a fourth or fth color is desired, according to conventional practice at least two of the electron beams must be utilized. If, for example, a cyan color is desired for a narrow vertical bar symbol, the blue and green beams are turned on momentarily by the video signal representing the cyan bar symbol. If there is no mis-convergence, the resulting blue and green bars on the phosphor screen are substantially superimposed and a single bar of cyan color appears. If there is substantial mis-convergence, the resulting blue and green bars appear spaced apart on the screen as two bars, one blue and one green. This can cause considerable confusion and error in the identication of symbols.

An object of the invention is to provide an improved method of and means for producing a color display.

A further object of the invention is to provide improved color display apparatus utilizing a multi-beam color tube in which difficulties ordinarily caused by misconvergence 'of the electron beams of the color tube are avoided.

A further object 'of the invention is to provide improved color display apparatus utilizing a three-color tube wherein symbols in more than three colors may be displayed with color accuracy even though the three electron beams of the color tube may be substantially misconverged.

In practicing one embodiment of the invention, a shadow mask color tube such as one of the type previ- 3,Zl5,'l7l Patented Nov. 2, 1965 ously identified, is employed. This is a three-gun tube, the electron beams from the three guns, respectively, impinging on red, blue and green phosphor dots, respectively, on the screen. The three guns are biased to obtain a medium value beam current from each gun so that as the beams scan the phosphor screen there is obtained a medium intensity white background. In photometric terms this is actually a white light background, although in conversational terms it might be referred to as gray because of the rather low level of illumination. The scanning may be at an ordinary television scanning rate. The white background is seen in spite of any mis-convergence since the colors produced on the screen by the three beams mix due, in the example assumed, to the scanning rate being at least equal to that of persistence of vision. For some applications of the invention the scanning may be at a rate less than that of persistence of vision providing the screen phosphors used have sucient lag or persistence. Stated somewhat differently, the white background is seen because during the time the beams scan the color screen without any change in beam intensity there is no reference point to identify the position of a beam at any given instant of time.

Under these conditions images or symbols may be obtained on the screen in six different colors as follows:

l. Positive video signal, representing a symbol, for example, fed to the red gun produces a red (desaturated red) symbol.

2. Negative video signal fed to the red gun produces a cyan image.

3. Positive video signal fed to the green gun produces a desaturated green image.

4. Negative video signal fed to the green gun produces a magnete image.

5. Positive video signal fed to the blue gun produces a desaturated blue image.

6. Negative video signal fed to the blue gun produces a yellow image.

Since the video signal is never applied to more than one gun at any one instant of time, for the reason that no two symbols are to appear one on top of the other, there can be no duplication of symbols or images in different colors when the video signal calls for only one symbol of one color. At the same time, symbols can be displayed in more colors than just the three primary colors.

The invention will be described in detail With reference to the accompanying drawing in which: 1

FIG. 1 is a schematic and block diagram illustrating one embodiment of the invention, and

FIG. 2 is a schematic and block diagram illustrating in more details certain parts of the apparatus shown in FIG. l.

In the several figures like parts are indicated by similar reference characters.

In FIG. 1 a tri-color kinescope, such as lone of the shadow-mask color tubes previously mentioned is indicated at 11. It has three electron guns 12, 13 and 14, each including a cathode 16 and a control grid 17. The three guns are biased so that as the three electron beams are deflected to scan the color screen (not shown) the light from the screen will be white light, but of a medium intensity. As a result, the picture background will have a -gray appearance.

FIG. 1 illustrates, by way of example, how symbols may be made to appear on the screen of the tri-color tube in six different colors, the video signal for a particular color symbol being applied to only one electron gun. Thus, a particular symbol cannot appear on the screen as two or three symbols side by side, and each of a different color, because of mis-convergence of the three electron beams. In the example, the symbol or symbols to be displayed in a particular color are on a motion picture film which is scanned by a flying spot scanner. The symbols that are to be displayed as red, cyan, green, magenta, blue and yellow symbols, respectively, are on films 1, 2, 3, 4, S and 6, respectively. These symbols may, for example, represent aircraft in the vicinity of an airport, the aircraft at one altitude level being displayed in one color and the aircraft at a different altitude level being displayed in a different color. These films may be driven intermittently in conventional fashion, as by a 2-3 intermittent motion commonly used in television transmission of motion picture film.

A drive for the film 1 is indicated at 21. Similar film drives (not shown) are provided to drive the other film 2 to 6, inclusive. Each film drive is driven by a synchronous motor connected to a 60-cycle power line, the motor for film drive 21 being shown at 22.

The fiying spot for scanning each film is produced on the screen of a cathode ray tube. This tube for scanning film 1 is shown at 23. The cathode ray of tube 23 is deflected horizontally and vertically by deliection circuits 24 and 26, respectively to produce a television type scan. The deection circuits are synchronized by horizontal and vertical synchronizing pulses supplied from a synchronizing pulse generator 27.

The generator 27 is phase locked to the 60 cycle power line whereby the film drives and the flying spot scanning are maintained in synchronism.

A photoelectric cell and amplifier unit picks up the light from the film being scanned to produce a video signal representing the symbol on film. This unit for the film 1 is indicated at 28. Similar photoelectric cell and amplifier units 29, 31, 32, 33 and 34 are provided for the other films 2 to 6, respectively. However, certain video outputs are made of positive polarity and others of negative polarity as will now be explained.

Since a symbol on film 1 is to be displayed as a red symbol on the screen of tri-color tube 11, the video signal from unit 28 is made of positive polarity. It is supplied over a lead 36 to the receiver where it passes through an amplifier 37 to the control grid of the red gun 12. This positive signal increases the intensity of the beam from the red gun whereby a red symbol appears on the color screen. This symbol appears against the gray (white light) background being laid down by the three beams scanning the color screen.

The three beams from guns 12, 13 and 14 are deflected by horizontal and vertical deflection circuits to scan the color screen in the usual television fashion. These deflection circuits, shown at 41 and 42, are synchronized with the fiying spot scanning by horizontal and vertical synchronizing pulses transmitted from the generator 27 over a line 43.

The symbols on film 2 are to be displayed as cyan symbols. Therefore, the video Signal from unit 29 is made of negative polarity. It is supplied over a lead 38 to the receiver where it passes through an amplifier 39 to the control grid of the red gun 12. This negative signal cuts off, or substantially cuts off, the beam from the red gun. Therefore, a cyan symbol appears on the color screen since blue and green are the only lcolors emitted from the color screen at the spot where the red beam was cut off. It is only at this spot that a cyan color can appear, i.e., at the spot determined by the cyan video signal.

The symbols on film 3 are to be displayed as green symbols. Therefore, the video signal from unit 31 is made of positive polarity. It is supplied over a lead 44 to the receiver where it passes through an amplifier 46 to the control grid of the green gun 13. This positive signal increases the intensity of the beam from the green gun whereby a green symbol appears on the color screen.

The symbols on film 4 are to be displayed as magenta symbols. Therefore, the video signal from unit 32 is made of negative polarity. It is supplied over a lead 47 to the receiver where it passes through an amplifier 48 to the control grid of the green gun 13. This negative signal cuts off, or substantially cuts off, the beam from the green gun. Therefore, a magental symbol appears on the color screen since red and blue are the only colors emitted from the color screen at the spot where the green beam was cut off. It is only at this spot that a magenta color can appear, i.e., at the spot determined by the magenta video signal.

The symbols on film 5 are to be displayed as blue symbols. Therefore, the video signal from unit 33 is made of positive polarity. It is supplied over a lead 49 to the receiver where it passes through an amplifier 51 to the control grid of the blue gun 14. This positive signal increases the intensity of the beam from the blue gun whereby a blue symbol appears on the color screen.

The symbols on film 6 are to be displayed as yellow symbols. Therefore, the video signal from unit 34 is made of negative polarity. It is supplied over a lead 52 to the receiver Where it passes through an amplifier 53 to the control grid of the blue gun 14. This negative signal cuts off, or substantially cuts off, the beam from the blue gun. Therefore, a yellow symbol appears on the color screen since red and green are the only colors emitted from the color screen at the spot where the blue beam was cut off. It is only at this spot that a yellow color can appear, i.e., at the spot determined by the yellow video signal.

Each of the video amplifiers 37, 39, etc., preferably is provided with means for adjusting its gain as indicated by the gain control knobs shown in FIG. 2.

FIG. 2 shows in more detail certain parts of the apparatus shown in FIG. 1. Referring to the three-gun shadow-mask tube 11, each of the three electron guns 12, 13 and 14 includes a cathode 16, a control grid 17, a screen grid 54, a focus electrode 56 and an anode 57.

A deflecting yoke 58 is provided for deflecting the three beams horizontally and vertically across the threecolor screen in accordance with usual television receiver practice.

The usual aquadag coating 59 is on the inside of the glass envelope. It is electrically connected to the aluminum backing layer of the screen (not shown), and both are maintained at a high voltage such as a voltage from 25 to 35 kilovolts. The three anodes 57 are electrically connected to each other and are each maintained at the same voltage as the aquadag coating. The cathodes of guns 12. 13 and 14 are held at ground potential.

Each of the control grids 17 is biased with respect t0 its cathode by means of a suitable circuit which may include direct current insertion means if desired. In the example illustrated, each control grid is negatively biased through a resistor connected to a variable tap on a potentiometer. Thus, the bias on each of the control grids for the guns 12, 13 and 14 may be adjusted by the adjustable taps 61, 62 and 73, respectively. The adjustment is such that, with no video signal present, the beam currents are in the mid-region of beam current; for example, at about 0.5 of full beam current.

Preferably, the usual provisions are made to obtain reasonably good convergence of the three electron beams. For example, dynamic convergence such as that employed in present commercial practice, may be employed as indicated schematically by the dynamic convergence cage 68. The three anodes 57 are mechanically supported by the cage 68, and all are' electrically connected by the cage so that they are maintained at 25 kv. in the example illustrated.

It should be understood that the invention is not limited to the use of shadow-mask color tubes. It may be employed, in general, with any multi-gun color tube. Also, it should be understood that the invention may be employed with any suitable source of video signals representative of the symbols or images to be displayed. For example, a computer output may be fed into a continuous video tape loop to generate the desired display.

Another example of the application of the invention to a multi-gun tube is its application to a two-gun color tube. Such a tube may be a shadow-mask color tube with a red gun and a green gun, the color screen having red and green phosphor dots. The two guns are biased so that their electron beams are at approximately onehalf full intensity so that as the color screen is scanned with no video signal applied the background is a medium brightness yellow raster. Symbols or images of four different colors may be displayed as follows:

Video signal of positive polarity applied to the red gun to increase beam intensity (to substantially full intensity, for example) produces an orange symbol.

Video signal of negative polarity applied to the red gun to decrease beam intensity (to substantially zero intensity, for example) produces a green symbol.

Video signal of positive polarity applied to the green gun to increase beam intensity (to substantially full intensity, for example) produces a yellow green symbol.

Video signal of negative polarity applied to the green gun to decrease beam intensity (to substantially Zero intensity, for example) produces a red symbol.

A three-gun color tube may be adjusted to give a dis-V play in ve colors by biasing one of the guns to cut-off, i.e., to substantially zero beam current, and adjusting the bias on the other two guns so that their beams are at about one-half full beam current, for example. Thus, the red and green guns may be adjusted as above described for a two-gun tube, and the blue gun adjusted to substantially zero beam current for the condition of no applied video signal. Video signals are applied to the red and green guns to obtain symbols in four colors as described above for the two-gun color tube operation. Symbols in a fifth color (blue) may be obtained by applying video signal to the blue gun with positive polarity to increase its beam intensity (to substantially full intensity, for example).

In one example of the adjustment of a three-gun shadow-mask tube for displaying symbols in ve colors as described above, the background brightness is adjusted to eight foot lamberts and the brightness of the symbols shown in a color, such as orange, produced by a full intensity beam is adjusted to twenty foot lamberts by adjustment of the amplitude of the positive video signal.

It will be apparent that the invention may be applid to color tubes having more than three guns. For example, it may be applied to a four-gun shadow-mask tube, there being a different color dot on the color screen for each gun. The adjustment and operation may be the same as previously described. For example, the four electron beams may be adjusted to about one-half full beam value to provide a medium intensity (gray) white background. Symbols in eight colors may then be displayed.

What is claimed is:

1. A display system comprising a multi-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit light of one color and the electron beam from another gun excites said screen to emit light of a different color, means for scanning said screen with the beams from at least two guns adjusted to have an intensity that, for the condition of no applied video signal, is in the mid-way region between zero intensity and full intensity, and means for applying a particular video signal to only one of said guns with a polarity to change its beam intensity to obtain a display of a single color.

2. A display system comprising a multi-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit light of one color and the electron beam from another gun excites said screen to emit light of a different color, means for scanning said screen with the beams from at least two of said guns adjusted to have an intensity that, for the condition of no applied video signal, is in the midway region between zero intensity and full intensity, means for applying a rst video signal to only one of said two guns with a polarity to increase its beam intensity to obtain a display of a lirst color, and means for applying a second video signal to only said one gun with a polarity to decrease its beam intensity to thereby obtain a display of a second color.

3. A display system comprising a multi-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit light of one color and the electron beam from another gun excites said screen to emit light of a different color, means for scanning said screen with the beams from at least two of said guns adjusted to have an intensity that, for the condition of no applied video signal, is in the midway region between zero intensity and full intensity, means for applying a first video signal to only one of said two guns with a polarity to increase its beam intensity to obtain a display of a rst color, means for applying a second video signal to only said one gun with a polarity to decrease its beam intensity to thereby obtain a display of a second color, means for applying a third video signal to another of said two guns only with a polarity to increase its beam intensity to obtain a display of a third color, and means for applying a fourth video signal to only said lastmentioned gun with a polarity to decrease its beam intensity to thereby obtain a display of a fourth color.

4. A display system comprising a multi-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit light of one color and the electron beam from another gun excites said screen to emit light of a different color, means for scanning said screen with the beams from said guns adjusted to have an intensity that, for the condition of no applied video signal, produces on the screen a background light level of medium intensity, means for applying a first video signal to only one of said guns with a polarity to increase its beam intensity to obtain a display of a rst color, means for applying a second Video signal to only said one gun with a polarity to decrease its beam intensity to thereby obtain a display of a second color, means for applying a third video signal to another of said guns only with a polarity to increase its beam intensity to obtain a display of a third color, and means for applying a fourth video signal to only said last-men tioned gun with a polarity to decrease its beam intensity to thereby obtain a display of a fourth color.

5. The method of operating a three-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit light of one color and the electron beams from the other guns each excite said screen to emit light of a different color, said method comprising scanning said screen with the beams from at least two of said guns adjusted to have an intensity that, for the condition of no applied video signal, is in the mid-way region between Zero intensity and full intensity, applying a particular video signal to only one of said two guns with a polarity to increase its beam intensity to obtain a display of one color, and applying a particular video signal to said one gun with a polarity to decrease its beam intensity to obtain a display of a second color.

6. The method of operating a three-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit light of one color and the electron beams from the other guns each excite said screen to emit light of a different color, said method comprising scanning lsaid screen with said beams adjusted to have an intensity that, for the condition of no applied video signal, is in the mid-way region between zero intensity and full intensity, applying a rst video signal to only one of said guns with a polarity to increase its beam intensity to obtain a display of color that is a desaturated color of that produced by said 1astmentioned beam alone, applying a second video signal to only said one gun with a polarity to decrease its beam intensity to thereby obtain a display of a second 'color that is produced by the mixture of the two colors produced by the other two beams, applying a third video Isignal to another of said guns only with a polarity to increase its beam intensity to obtain a display of a color that is a desaturated color of that produced by said last-mentioned beam alone, and applying a fourth video signal to only said last-mentioned gun with a polarity to decrease its beam intensity to thereby obtain a display of a fourth color that is produced by the mixture of the two colors produced by the other two beams.

7. A display system comprising a three-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit a light of one color and the electron beams from the other guns each excite said screen to emit light of a different color, means for scanning said screen with the beams from at least two of said guns adjusted to have an intensity that, for the condition of no applied Video signal, is in the mid-Way region between zero intensity and full intensity, means for applying a first video signal to only one of said guns with a polarity to increase its beam intensity to obtain a display of a first color, means for applying a second video signal to only said one gun with a polarity to decrease its beam intensity substantially to zero to thereby obtain a display of a second color, means for applying a third video signal to another of said guns only with a polarity to increase its beam intensity to obtain a display of a third color, and means for applying a fourth video signal to only said last-mentioned gun with a polarity to decrease its beam intensity substantially to Zero to thereby obtain a display of a fourth color.

8. A display system comprising a three-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit light of one color and the electron beams from the other guns each excite said screen to emit light of a different color, means for scanning said screen with said beams adjusted to have an intensity that, for the condition of no applied video signal, produces on the screen a white light to display of medium intensity, means for applying a rst video signal to only one of said guns with a polarity to increase its beam intensity to obtain a display of a color that is a desaturated color of that produced by said last-mentioned beam alone, means for applying a second video signal to only said one gun with a polarity to decrease its beam intensity to thereby obtain a display of a second color that is produced by the mixture of the two colors produced by the other two beams, means for applying a third video signal to another of said guns only with a polarity to increase its beam intensity to obtain a display of a color that is a desaturated color of that produced by said last-mentioned beam alone, and means for applying a fourth video signal to only said last-mentioned gun with a polarity to decrease its beam intensity to thereby obtain a display of a fourth color that is produced `by .the mixture of the two colors produced by the other two beams.

9. A display system comprising a three-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit light of one color and the electron beams from the other guns each excite said screen to emit light of a different color, said beams being at least approximately converged, means for scanning said screen with said beams adjusted to have an intensity that, for the condition of no applied video signal, produces on the screen a white light display of medium intensity, means for applying a first video signal to only one of said guns with a polarity to increase its beam intensity to obtain a display of a color that is a .desaturated color of that produced by said last-mentioned beam alone, means for applying a second video signal to only said one gun with a polarity to decrease its beam intensity substantially to zero to thereby obtain a display of a second color that is produced by the mixture of the two colors produced by the other two beams, means for applying a third video signal to another of said guns only with a polarity to increase its beam intensity to obtain a display of a color that is a desaturated color of that produced by said last-mentioned beam alone, and means for applying a fourth video signal to only said last-mentioned gun with a polarity to decrease its beam intensity substantially to zero to thereby obtain a display of a fourth color that is produced by the mixture of the two colors produced by the other two beams.

10. A display system comprising a three-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit light of one color and the electron beams from the other guns each excite said screen to emit light of a different color on said screen, means for scanning said screen with the beams from at least two of said guns adjusted to have an intensity that, for the condition of no applied video signal, is in the mid-way region between zero intensity and full intensity, means for applying a first video signal to only one of said two guns with a polarity to increase its beam intensity to obtain a display `of a first color, means for applying a second video signal to only said one gun with a polarity to decrease its beam intensity to thereby obtain a display of a second color, means for applying a third video signal to the other of said two guns only with a polarity to increase its beam intensity to obtain a display of a third color, means for applying a fourth video signal to only said last-mentioned gun with a polarity to decrease its beam intensity to thereby obtain a display of a fourth color, and means for applying a fifth video signal to only the remaining one of said guns with a polarity to increase its beam intensity to obtain a display of a fth color.

1l.. A display system comprising a three-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit light of one color and the electron beams from the other guns each excite said screen to emit light of a different color, means for scanning said screen with said beams adjusted to have an intensity that, for the condition 0f no applied video signal, produces on the screen a background light level of medium intensity, means for applying a iirst video signal to only one of said guns with a polarity to increase its beam intensity to obtain a display of a color that is a desaturated color of that produced by said last-mentioned beam alone, means for applying a second video signal to only said one gun with a polarity to decrease its beam intensity to thereby obtain a display of a second color that is produced by the mixture of the two colors produced by the other two beams, means for applying a third video signal to another of said guns only with a polarity to increase its beam intensity to obtain a display of a color that is a desaturated color of that produced by said last-mentioned beam alone, means for applying a fourth video signal to only said last-mentioned gun with a polarity to decrease its beam intensity to thereby obtain a display of a fourth color that is produced by the mixture of the two colors produced by the other two beams, means for applying a fifth video signal to only the remaining one of said guns With a polarity to increase its beam intensity to obtain a display of a color .that is a desaturated color of that produced by the beam from said remaining gun alone, and means for applying a sixth video signal to only said remaining gun with a polarity to decrease its beam intensity to thereby obtain a display of a Sixth color that is produced by the mixture of the two colors produced by the other two beams.

12. A display system comprising a three-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit light of one color and the electron beams from the other guns each excite said screen to emit light of a different color, means for scanning said screen with said beams adjusted to have an intensity that, for the condition of no applied video signal, produces on the screen a white light display of medium intensity, means for applying a rst video signal to only one of said guns with a polarity to increase its beam intensity to obtain a display of a color that is a desaturated color of that produced by said last-mentioned beam alone, means for applying a second video signal to only said one gun with a polarity to decrease its beam intensity to thereby obtain a display of a second color that is produced by the mixture of the two colors produced by the other two beams, means for applying a third video signal to another of said guns only with a polarity to increase its beam intensity to obtain a display of a color that is a desaturated color of that produced by said last-mentioned beam alone, means for applying a fourth video signal to only said last-mentioned gun with a polarity to decrease its beam intensity to thereby obtain a display of a fourth color that is produced by the mixture of the two colors produced by the other two beams, means for applying a fifth video signal to only the remaining one of said guns with a polarity to increase its beam intensity to obtain a display of a color that is a desaturated color of that produced by the beam from said remaining gun alone, and means for applying a sixth Video signal to only said remaining gun with a polarity to decrease its beam intensity to thereby obtain a display of a sixth color that is produced by the mixture of the two colors produced by the other two beams.

13. A display system comprising a three-gun color tube having a color screen and being of the type wherein the electron beam from one gun excites said screen to emit light of one color and the electron beams from the other guns each excite said screen to emit light of a different color, means for scanning said screen with said beams adjusted so that for the condition of no applied video signal two of said beams have an intensity that is in the mid-way region between z'ero intensity and full intensity and the third of said beams has substantially zero intensity, means for applying a rst video signal to only one of said two guns with a polarity to increase its beam intensity to obtain a display of a first color, means for applying a second video signal to only said one gun with a polarity to decrease its beam intensity to thereby obtain a display of a second color, means for applying a third video signal to the other of said two guns only with a polarity to increase its beam intensity to obtain a display of a third color, means for applying a fourth video signal to only said last-mentioned gun with a polarity to decrease its beam intensity to thereby obtain a display of a fourth color, and means for applying a ifth video signal to only the remaining one of said guns with a polarity to increase its beam intensity to obtain a display of a fifth color.

References Cited by the Examiner RCA Victor, Technical Features of the RCA Victor Model 21CT55 Color Television Receiver, copyrighted 1954, pages 13 and 14 cited.

DAVID G. REDINBAUGH, Primary Examiner. ROBERT SEGAL, Examiner. 

1. A DISPLAY SYSTEM COMPRISING A MULTI-GUN COLOR TUBE HAVING A COLOR SCREEN AND BEING OF THE TYPE WHEREIN THE ELECTRON BEAM FROM ONE GUN EXCITIES SAID SCREEN TO EMIT LIGHT OF ONE COLOR AND THE ELECTRON BEAM FROM ANOTHER GUN EXCITIES SAID SCREEN TO EMIT LIGHT OF A DIFFERENT COLOR, MEAN FOR SCANNING SAID SCREEN WITH THE BEAMS FROM AT LEAST TWO GUNS ADJUSTED GO HAVE AN INTENSITY THAT, FOR THE CONDITION OF NO APPLIED VIDEO SIGNAL, IS IN THE MID-WAY REGION BETWEEN ZERO INTENSITY AND FULL INTENSITY, AND MEANS FOR APPLYING A PARTICULAR VIDEO SIGNAL TO ONLY ONE OF SAID GUNS WITH A POLARITY TO CHANGE ITS BEAM INTENSITY TO OBTAIN A DISPLAY OF A SINGLE COLOR. 